PATHOLOGY

Detailed explanation-1: -Answer and Explanation: The hollow mass of cells in the early stages of embryonic development is called the blastula.

Detailed explanation-2: -In mammals, the blastocyst contains an embryoblast (or inner cell mass) that will eventually give rise to the definitive structures of the fetus, and a trophoblast which goes on to form the extra-embryonic tissues.

Detailed explanation-3: -Three days after fertilization, a normally developing embryo will contain about six to 10 cells. By the fifth or sixth day, the fertilized egg is known as a blastocyst-a rapidly dividing ball of cells. The inner group of cells will become the embryo. The outer group will become the cells that nourish and protect it.

Detailed explanation-4: -The embryonic stage consisting of a hollow ball of cells is called the blastula formation.